JPH03203982A - Organic electric field luminous element - Google Patents

Abstract

PURPOSE:To provide the subject luminous element having excellent luminance and useful for displays by adding a specific compound having a naphthylidine skeleton to an organic electric field luminous element in which an organic positive hole injection transportation layer and an organic luminous layer are disposed between electrodes comprising electro-conductive layers. CONSTITUTION:A compound whose naphthylidine skeleton of formula I or II has at least one group selected from aromatic homocyclic groups and aromatic heterocyclic groups directly or through any other group is added to an organic luminous layer 4 in an organic electric field luminous element which is prepared by laminating a positive hole injection transportation layer 3 and an organic luminous layer 4 between an electro-conductive layer 2a (e.g. aluminum; anode; a visible light transmittance of preferably >=60%; a membrane thickness of preferably 50-10000Angstrom ) and an electro-conductive layer 2b (e.g. tin; cathode; a membrane thickness of preferably 100-5000Angstrom ) on a substrate (e.g. quartz) 1 as a support for the electric field luminous element, thereby providing the objective luminous element.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an organic electroluminescent device, and more specifically, it emits light by applying an electric field through a combination of a hole injection transport layer and a light emitting layer made of an organic compound. The present invention relates to a thin film device that emits .

(Prior art) Conventionally, thin-film electroluminescent devices have been made using inorganic materials such as n-
ZnS, CaS, SrS, which are Vt group compound semiconductors
Mn and rare earth elements (Eu, Ce,
Electroluminescent devices made from the above-mentioned inorganic materials are generally doped with Tb, S+++), but electroluminescent devices made from the above-mentioned inorganic materials require 1) alternating current driving (~1 kHz), 2) high driving voltage (
~200V), 3) It is difficult to achieve full color, and 4) The cost of peripheral drive circuits is high.

However, in recent years, in order to improve the above problems, electroluminescent devices using organic materials have been developed. Dyes (J, Chem, Soc
, ,Chem,C.

mmun, 557.1985), pyrazoline (Mo
1.Crys t,ttq,Crys t,.

135.355. (1986)), Perylene (Jp
n, J. Appl, Phys., 25. L773,
(1986)), coumarin-based compounds, and tetraphenylbutadiene (JP-A-57-51781). , Optimization of electrode types and creation of a light-emitting layer consisting of a front plate injection transport layer and an organic phosphor (Japanese Patent Application Laid-Open No. 57-51781.59-
194393.63-295695).

(Problems to be Solved by the Invention) However, the organic electroluminescent devices disclosed by these methods still have insufficient luminous performance, and further improvement studies are desired.

An object of the present invention is to provide an organic electroluminescent device using an organic light-emitting substance that can emit light with high brightness even at a low driving voltage.

(Means for Solving the Problems) That is, the gist of the present invention is to provide an organic electroluminescent device in which an organic hole injection transport layer and an organic light emitting layer are provided between electrodes consisting of two conductive layers. Organic electroluminescence characterized by containing a compound having at least one group selected from an aromatic hydrocarbon ring group and an aromatic heterocyclic group directly or via another group in the naphthyridine skeleton represented by It exists in the element.

Hereinafter, the electroluminescent device of the present invention will be explained with reference to the accompanying drawings. 1 and 2 are cross-sectional views schematically showing an example of the structure of the electroluminescent device of the present invention, in which 1 is a substrate, 2a,
2b represents a conductive layer, 3 represents a hole injection transport layer, 4 represents a light emitting layer, and 5 represents an electron injection transport layer.

The substrate 1 serves as a support for the electroluminescent device of the present invention, and may be a quartz or glass plate, a metal plate or metal foil, a plastic film or sheet, and may be a glass plate, polyester, polymethacrylate, Transparent synthetic resin substrates such as polycarbonate and polysulfone are preferred.
A conductive layer 2a is provided on the substrate 1;
A is usually a metal such as aluminum, gold, silver, nickel, palladium, tellurium, a metal oxide such as indium and/or tin oxide, copper iodide, carbon black, or poly(3-methylthiophene). It is made of conductive resin such as.

The conductive layer is usually formed by sputtering, vacuum evaporation, etc., but it can also be formed using fine metal particles such as silver, copper iodide, carbon black, conductive metal oxide fine particles, conductive resin fine powder, etc. In some cases, it can also be formed by dispersing it in a suitable binder resin solution and coating it on the substrate. Furthermore, in the case of conductive resin, a thin film can be formed directly on the substrate by electric field polymerization.

The above conductive layer can also be laminated with different materials. The thickness of the conductive layer 2a varies depending on the required transparency, but if transparency is required, the visible light transmittance is 6.
It is desirable to transmit 0% or more, preferably 80% or more, and in this case, 50 to 10,000 people, preferably 100
~5000 people. Conductive layer 2 if opaque is acceptable
a may be the same as the substrate l, and furthermore, it is also possible to laminate the above-mentioned conductive layers with different materials.

In the example shown in FIG. 1, the conductive layer 2a serves as an anode to inject holes.

On the other hand, the conductive layer 2b plays a role of injecting electrons into the light emitting layer 4 as a cathode. The material used for the conductive layer 2b can be the same as the material for the conductive layer 2a, but in order to efficiently inject electrons, metals with a low work function are preferred, such as tin, magnesium, and indium. , aluminum, silver, or an alloy thereof. The thickness of the conductive layer 2b is usually the same as that of the conductive layer 2a. Further, although not shown in FIG. 1, a substrate similar to substrate 1 may be further provided on the conductive layer 2b. However, as an electroluminescent device, it is necessary that at least one of the conductive layers 2a and 2b has good transparency. From this, one of the conductive layers 2a and 2b has 10
The film thickness is preferably 0 to 5000, and good transparency is desired.

A hole injection transport layer 3 is provided on the conductive layer 2a,
The hole injection transport layer 3 is formed of a compound that can efficiently transport holes from the anode toward the light emitting layer between the electrodes to which an electric field is applied.

The hole injection/transport compound needs to be a compound that has high hole injection efficiency from the conductive layer 2a and can efficiently transport the injected holes. To this end, it is required that the compound has a low ionization potential, high hole mobility, excellent stability, and is unlikely to generate trapping impurities during production or use.

Such hole injection and transport compounds are described, for example, in JP-A-59-
194393, pages 5-6 and U.S. Patent No. 417596.
Examples include those explained in columns 13 to 14 of No. 0. Preferred specific examples of these compounds include N, N'
-diphenyl-N.

N'-(3-methylphenyl)-1,1'-biph22-4,4'-diamine: 1,1'-bis(4-di-p-
) lylaminophenyl) cyclohexane: Aromatic amine compounds such as 4.4'-bis(diphenylamino)quadrophenyl are mentioned.

The hole injection transport layer 3 is formed by laminating it on the conductive layer 2a by a coating method or a vacuum evaporation method.

In the case of coating, a coating solution containing one or more hole-injecting and transporting compounds and, if necessary, additives such as a binder resin that does not trap holes and a coating properties improver such as a leveling agent, is used. It is adjusted, coated on the conductive layer 2a by a method such as a spin code method, and dried to form the hole injection transport layer 3. Examples of the binder resin include polycarbonate, polyarylate, polyester, and the like. If the binder resin is added in a large amount, the hole mobility will be reduced, so a smaller amount is preferable, and 50% by weight or less is preferable.

The thickness of the hole injection transport layer is usually 100 to 3000, preferably 300 to 1000. Vacuum deposition is often used to uniformly form such thin films.

In FIG. 1, an organic light-emitting layer 4 is typically laminated on a hole injection transport layer 3. This layer simultaneously serves the role of transporting electrons from the conductive layer 2b toward the hole injection transport layer 3 and the role of causing light emission when holes and electrons are recombined. Aromatic compounds such as tetraphenylbutadiene and coumarin (Japanese Unexamined Patent Application Publication No. 1989-1999) are examples of materials that have both roles.
7-51781) and metal complexes such as aluminum complexes of 8-hydroxyquinoline (JP-A-59-194393)
Examples include.

In FIG. 2, an electron injection transport layer 5 is provided between the organic light emitting layer 4 and the conductive layer 2b as a measure to increase the efficiency of light emission. It is believed that the electron injection and transport layer 5 plays a role in efficiently injecting electrons from the conductive layer 2b and at the same time transporting the injected electrons toward the light emitting layer 4. This structure is characterized in that the compound used in the light emitting layer 4 does not need to have electron transport ability.

The electroluminescent device of the present invention uses a compound in which the naphthyridine skeleton has at least one group selected from an aromatic hydrocarbon ring group or an aromatic heterocyclic group directly or via another group as the above-mentioned organic light-emitting compound. It is characterized by containing.

To explain in more detail the naphthyridine skeleton compound used in the present invention, in the following general formula (I) or (II), at least one of A, B, C, D, E and F, or A', B' , C', D', E' and F' is a compound having an aromatic hydrocarbon ring group or an aromatic heterocyclic group directly or through another group. .

Specifically, as an example of a case where the groups AF and A' to F' directly have an aromatic group, A.

at least one of B, C, D, E and F or less of A', B', C', D', E' and F' (
One of them is an aromatic hydrocarbon ring group such as a phenyl group, an acenaphthyl group, an anthryl group, a phenanthryl group, or a group in which these groups have a substituent, and/or a thienyl group, a pyrrolyl group, a thiazolyl group, or a furyl group. group, carbazolyl group, oxacylyl group, benzothienyl group, benzofuryl group, benzoxasilyl group, indolyl group, pyridyl group, quinolyl group, and aromatic heterocyclic groups such as groups in which these groups have a substituent. Compounds representing groups such as

Substituents for these groups include halogen atoms such as chlorine atom, bromine atom, and iodine atom; alkyl groups having 1 to 6 carbon atoms such as methyl group and ethyl group; 1 to 6 carbon atoms such as methoxy group and ethoxy group; Alkoxy group: methoxycarbonyl group,
Alkoxycarbonyl group having an alkoxy group having 1 to 6 carbon atoms, such as ethoxycarbonyl group; alkoxysulfonyl group having an alkoxy group having 1 to 6 carbon atoms, such as methoxysulfonyl group, ethoxysulfonyl group, diano group, amino group, dimethylamino group , nitro group, etc.

In addition, examples of cases where A-F, A' to F' have an aromatic group via another group include A, B, C,
at least one of D, E and F or A', B',
At least one of C', D', E' and F' is -
CONIIR, -CONRR', -GOOR (wherein R represents an aromatic hydrocarbon ring group such as a phenyl group, a naphthyl group, or a group substituted with these groups, and R' represents an aromatic hydrocarbon ring group such as a phenyl group, a naphthyl group, or a group substituted with these groups) or an optionally substituted alkyl group), or a group having at least one aromatic hydrocarbon ring group and an aromatic heterocyclic group in a group such as a benzoyl group. Examples include the compounds shown below.

These aromatic hydrocarbon ring groups or aromatic heterocyclic groups are preferably substituted or unsubstituted phenyl groups. Further, when B and C, E and F, B' and C' and E' and F' simultaneously represent an aromatic hydrocarbon ring group or an aromatic heterocyclic group, it is better that both are not bulky groups at the same time.

In the compound of the general formula (I) or (n) used in the present invention, A, B, C, D, E and F or A', B'
, C', D', E' and F', specific examples of groups other than the aromatic hydrocarbon ring group and the aromatic heterocyclic group explained above include -CONHz, - CONHR
", -CONR"R", -COOR" (wherein, Ra,
Hat indicates an alkyl group that may be substituted), a nitro group, a cyano group, a halogen atom such as a chlorine atom, a bromine atom, an iodine atom, an alkyl group having 1 to 28 carbon atoms, a vinyl group, an allyl group Examples include alkenyl groups, carboxyl groups, acetyl groups, etc.

In general formulas (1) and (II), A-F, A' to F'
Although it is possible to have up to six aromatic groups at the substitution positions, the compounds used in the present invention have A, B, C, E
Preferably, the compound exhibits at least aromatic substituents at the four positions A', B', C', and E'.

Synthesis methods for these compounds are described by Mataga et al., J.

Heterocyclic, Chem, Volume 20, 9
71 (1983).

Specific examples of such compounds used in the present invention are represented by the following formula (
Examples are shown in III) to (XX).

1113 ■υ: These compounds exhibit strong fluorescence and are suitable as compounds for organic light-emitting layers.

The thickness of the organic light emitting layer 4 is usually 100 to 2000, preferably 300 to 1000.

The organic light emitting layer 4 can also be formed by the same method as the hole injection transport layer, but usually a vacuum evaporation method is used. Organic thin films formed by vacuum evaporation often aggregate and deteriorate after being left for a long period of time, but the organic light-emitting compound of the present invention is also excellent in this respect.

The thickness of the electron injection transport layer 5 further provided on the organic light emitting layer is usually 30 to 1000, preferably 50 to 300.
It's a person. Examples of the compound used in the electron injection transport layer 5 include the aforementioned tetraphenylbutadiene and an Al complex of 8-hydroxyquinoline.

It should be noted that the structure is opposite to that shown in FIG.
b. It is also possible to laminate the organic light emitting layer 4, the hole injection transport layer 3, and the conductive layer 2a in this order, and as described above, the electric field of the present invention can be formed between two substrates, at least one of which is highly transparent. It is also possible to provide a light emitting element. Similarly, the structure may be reversed to that shown in FIG. 2, that is, the conductive layer 2b, the electron injection transport layer 5, the organic light emitting layer 4, the hole injection transport layer 3, and the conductive layer 2a may be laminated in this order on the substrate. It is possible.

(Effect of the invention) According to the electroluminescent device of the invention, the conductive layer (anode)/
Hole injection transport layer / light emitting layer / conductive layer (cathode) or conductive layer (anode) / hole injection transport layer / light emitting layer / electron injection transport layer / conductive layer (cathode) are sequentially deposited on the substrate, Moreover, because a specific compound is used in the light emitting layer,
When a voltage is applied using both groove electrode layers as electrodes, yellow light emission with sufficient brightness for practical use can be obtained with a low driving voltage.

Therefore, the electroluminescent device of the present invention can be used in the field of flat panel displays (for example, wall-mounted televisions), or as a light source that takes advantage of its characteristics as a surface light emitting device (for example, light sources for copying machines, Buffklight light sources for liquid crystal displays, instruments, etc.). display board,
It can be applied to marker lights, and its technical value is great.

(Examples) Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the description of the following Examples unless it exceeds the gist thereof.

Example 1 An electroluminescent device having the structure shown in FIG. 1 was manufactured.

After 1,200 indium tin oxide (ITO) transparent conductive films were deposited on a glass substrate and ultrasonically cleaned with toluene and isopropyl alcohol, A
The surface was cleaned by exposing it to a glow discharge of r for 1 minute.

Thereon, as a hole injection transport layer, an aromatic amine compound represented by the following structural formula (1) was deposited to a thickness of 750 nm by vacuum evaporation.

The degree of vacuum was 1X10-'Torr.

Next, as an organic light emitting layer, a compound represented by formula (III) was deposited to a thickness of 500 nm in the same manner as the hole injection transport layer.

Furthermore, as an electron transport layer, 8-
100A of AJ complex of hydroxyquinoline! I arrived.

In the vapor deposition, the aromatic amine compound is placed in a ceramic crucible, the area around the crucible is heated with a Ta ray heater, and the vapor deposition source is evaporated in a vacuum container. Finally, during vapor deposition, an alloy electrode of magnesium and silver was used as a cathode, each with a film thickness ratio of 1O2.
:1, the film thickness was 2,000 yen by simultaneous evaporation. Vapor deposition was carried out using a molybdenum boat, and the degree of vacuum was 1.
A glossy electrode was obtained at x10-'T o r r.

In this way, an electroluminescent device having the structure shown in FIG. 2 was prepared, and when a DC voltage of 30 V was applied as a positive voltage to the ITO electrode (anode) and a negative voltage to the magnesium-silver electrode (cathode) of this device, 156 (c d
Uniform light emission was confirmed at a brightness of 57 mA/m"). This light emission was yellow and had a peak wavelength of 570 nm. Also, the current density flowing through the device at this time was 57 (mA/am"), and the light emission was yellow with a peak wavelength of 570 nm. The efficiency was 0.029 (j!m/W). The threshold voltage for light emission (the voltage at which the luminance is 1 (c d 7 m'')) was 16V.

Example 2 On a glass ITO substrate cleaned in the same manner as in Example 1, an aromatic amine compound represented by the formula
The compound shown in ir) was deposited to a thickness of 500 ml.

Further, as an electron transport layer, an Al complex of 8-hydroxyquinoline shown in formula (2) above was vapor-deposited, and a cathode was vapor-deposited in the same manner as in Example 1. An organic electroluminescent device having the structure shown in FIG. I got it.

When a DC voltage of 24 V was applied in the same manner as in Example 1, uniform light emission was confirmed with a brightness of 131 (c d 7 m"). This light emission was yellow and had a peak wavelength of 570 nm.
It was m. Also, the current density flowing through the element at this time is 2
6 (m A /3”l, luminous efficiency is 0.06 (j
m/W), and the threshold voltage for light emission (brightness of 1
(voltage indicating cd/m'') was 14V.

[Brief explanation of drawings]

1 and 2 are cross-sectional views of examples of the electroluminescent device of the present invention, in which 1 is a substrate, 2a and 2b are conductive layers, 3 is a hole injection transport layer, and 4 is a The light emitting layer 5 represents an electron injection transport layer. No. 1, No. 2, Applicant: Mitsubishi Kasei Corporation

Claims (1)

[Claims] An organic electroluminescent device in which an organic hole injection transport layer and an organic light emitting layer are provided between electrodes made of two conductive layers,
The naphthyridine skeleton shown in the structural formula below has at least one group selected from aromatic hydrocarbon ring groups and aromatic heterocyclic groups, either directly or through another group. 1. An organic electroluminescent device characterized by containing a compound.